ΔG° and TΔS° charge relationships for the binding of carboxylic anions by open-chain polyammonium cations

Abstract

Enthalpies of formation have been determined by titration calorimetry for complexes formed by some polycarboxylic anions (citrate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate) with open-chain polyammonium cations C_2(n-1)N_nH_(6n-2)ⁿ⁺ (n=2–6), at 25°C. ΔH° values are generally positive and, therefore, these complexes are entropically stabilized. ΔG° and TΔS° follow a linear trend as a function of polyammonium cation and carboxylic anion charges. The linear dependence on charges of ΔG° is the same for different systems, whilst that of TΔS° is specific for each system. ΔG° and TΔS° charge relationships are reported.